I am installing a metal roof over old shingles. I have been told to install 1x4 purlins for ventilation.

Question

The 1x4s also to provide a flat surface for better installation.

The question is: Do I need to install a vapor barrier over the purlins before installing the metal roof?

Answer 1

I would say no.I have helped out on installing 2 metal roofs in my neighborhood.One of them was a stripped clean roof with Tyvek, and the other was just like yours, over composition shingles.I would, however get another opinion, as we are not professional Metal Roofers.These jobs were 5+ years ago, with no problems. 8/02